net/bridge/netfilter/ebt_snat.c

   1 /*
   2  *  ebt_snat
   3  *
   4  *      Authors:
   5  *      Bart De Schuymer <bdschuym@pandora.be>
   6  *
   7  *  June, 2002
   8  *
   9  */
  10
  11 #include <linux/netfilter.h>
  12 #include <linux/netfilter_bridge/ebtables.h>
  13 #include <linux/netfilter_bridge/ebt_nat.h>
  14 #include <linux/module.h>
  15 #include <net/sock.h>
  16 #include <linux/if_arp.h>
  17 #include <net/arp.h>
  18
  19 static int ebt_target_snat(struct sk_buff *skb, unsigned int hooknr,
  20    const struct net_device *in, const struct net_device *out,
  21    const void *data, unsigned int datalen)
  22 {
  23         const struct ebt_nat_info *info = data;
  24
  25         if (!skb_make_writable(skb, 0))
  26                 return EBT_DROP;
  27
  28         memcpy(eth_hdr(skb)->h_source, info->mac, ETH_ALEN);
  29         if (!(info->target & NAT_ARP_BIT) &&
  30             eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
  31                 const struct arphdr *ap;
  32                 struct arphdr _ah;
  33
  34                 ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
  35                 if (ap == NULL)
  36                         return EBT_DROP;
  37                 if (ap->ar_hln != ETH_ALEN)
  38                         goto out;
  39                 if (skb_store_bits(skb, sizeof(_ah), info->mac,ETH_ALEN))
  40                         return EBT_DROP;
  41         }
  42 out:
  43         return info->target | ~EBT_VERDICT_BITS;
  44 }
  45
  46 static int ebt_target_snat_check(const char *tablename, unsigned int hookmask,
  47    const struct ebt_entry *e, void *data, unsigned int datalen)
  48 {
  49         const struct ebt_nat_info *info = data;
  50         int tmp;
  51
  52         if (datalen != EBT_ALIGN(sizeof(struct ebt_nat_info)))
  53                 return -EINVAL;
  54         tmp = info->target | ~EBT_VERDICT_BITS;
  55         if (BASE_CHAIN && tmp == EBT_RETURN)
  56                 return -EINVAL;
  57         CLEAR_BASE_CHAIN_BIT;
  58         if (strcmp(tablename, "nat"))
  59                 return -EINVAL;
  60         if (hookmask & ~(1 << NF_BR_POST_ROUTING))
  61                 return -EINVAL;
  62
  63         if (tmp < -NUM_STANDARD_TARGETS || tmp >= 0)
  64                 return -EINVAL;
  65         tmp = info->target | EBT_VERDICT_BITS;
  66         if ((tmp & ~NAT_ARP_BIT) != ~NAT_ARP_BIT)
  67                 return -EINVAL;
  68         return 0;
  69 }
  70
  71 static struct ebt_target snat __read_mostly = {
  72         .name           = EBT_SNAT_TARGET,
  73         .target         = ebt_target_snat,
  74         .check          = ebt_target_snat_check,
  75         .me             = THIS_MODULE,
  76 };
  77
  78 static int __init ebt_snat_init(void)
  79 {
  80         return ebt_register_target(&snat);
  81 }
  82
  83 static void __exit ebt_snat_fini(void)
  84 {
  85         ebt_unregister_target(&snat);
  86 }
  87
  88 module_init(ebt_snat_init);
  89 module_exit(ebt_snat_fini);
  90 MODULE_DESCRIPTION("Ebtables: Source MAC address translation");
  91 MODULE_LICENSE("GPL");